The present invention relates to a process and apparatus for the sulfonation of organic reactants and particularly to an improved process and apparatus for the production of sulfonic acids such as alkyl diaryl ether disulfonic acid, alkyl diaryl disulfonic acid, high molecular weight alkyl aryl sulfonic acids, dialkyl aryl sulfonic acid and other sulfonic acids characterized by high viscosities at reaction conditions as compared to dodecylbenzene sulfonic acid.
The terms "sulfonation" and "sulfonating" as employed herein are used sometimes in their generic sense as applying both to true sulfonating and to sulfating, and sometimes in its specific sense, that is to true sulfonating. Where the context in which the terms "sulfonation" and "sulfonating" are used does not require the specific sense, it is to be construed generically.
Organic sulfonic acids and organic sulfonates are important commercially as components of detergents. Of interest to the present application is the disclosure of co-owned U.S. Pat. No. 3,620,684 to Brooks, et al. This patent discloses an improved method and apparatus for the sulfonation of organic reactants by means of a reaction between a liquid organic reagent and sulfur trioxide vapor in a thin-film reactor. The apparatus for carrying out the reaction comprises two externally cooled, concentric circular reaction surfaces, the space between the reaction surfaces being one-eighth to one-half inch; a rotor located concentrically between the two reaction surfaces, the clearance between the rotor and the reaction surfaces being five- to forty-thousandths (0.005 to 0.040) of an inch; means for turning the rotor; and means for passing the reactant liquid and the reactant gas in parallel streams to the space between the said reaction surfaces and the rotor. Also of interest is the disclosure of Falk, et al., U.S. Pat. No. 2,923,728 relating to a process of reacting organic compounds with sulfur trioxide.
Other methods for the sulfonation of organic products include the use of what are known in the art as "jet-reactors." See Brooks, et al., U.S. Pat. No. 4,113,438. The use of both thin-film and jet reactors for the sulfonation of organic reagents is generally suitable for reaction of reactants whose sulfonic acids have relatively low viscosities (10 to 1000 cps with a maximum of 1,500 cps at the temperature of reaction). The use of such reactors is limited, however, in cases where the sulfonation reaction produces a sulfonic acid having a high viscosity at the reaction temperature. Sulfonation products such as alkyl diphenyl ether disulfonic acid (ADEDS) are characterized by viscosities ranging from 1,500 cps to 40,000 cps at reaction temperature (about 200.degree. F). ADEDS is particularly useful as an additive in household detergent formulations as well as a surfactant in many industrial detergent applications. As a detergent, ADEDS is characterized by excellent properties including high thermal stability, high solubility and the ability to solubilize other detergents. When produced according to conventional methods, however, ADEDS is generally unsuitable for household use because of residual processing impurities. Another sulfonation product characterized by high viscosity is high molecular weight alkyl benzene sulfonic acid (ABS) with an alkyl group of 18 or more carbons. ABS is particularly useful as a non-aqueous detergent such as an additive for high temperature lubricating oil. Another sulfonation product characterized by high viscosity is dialkyl naphthalene sulfonic acid (DANS) with each alkyl group containing 5 or more carbons. In its neutral form, DANS is particularly useful as a corrosion inhibiting agent.
All of the above described sulfonic acids are currently produced with batch solvent reaction systems. Most solvents used in such systems are hazardous materials which must be contained, recovered and in some cases must be removed from the product because even small amounts remaining in the product are undesirable. Unfortunately, complete removal of such solvents from the product is extremely difficult if not impossible.
In the case of currently used film reactors, the thick films of high viscosity reaction products prevent sufficient penetration of the sulfur trioxide through the thickness of the reaction product to the unreacted feedstock to give sufficient yields of reaction products. Efforts to increase yields of the sulfonation reaction by means of applying higher temperatures or higher mole ratios of sulfur trioxide have generally proven to be of limited use. Addition of acetic acid is known to increase the reaction yields as is known with other alkyl aryl feedstocks.